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authorLinus Torvalds <torvalds@linux-foundation.org>2018-04-28 10:06:16 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2018-04-28 10:06:16 -0700
commita97d8efd9d350bd9c6cf13689c7cc09049b42acd (patch)
tree6159a9faa50938c01cab75fd0bab4313a9c92247 /Documentation
parent6e041ffcc2d0bf8792937e89480b2172a9dd2823 (diff)
parent2a010461207cc96bee5ab81748325dec1972976f (diff)
Merge branch 'i2c/for-current' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux
Pull i2c fixes from Wolfram Sang: - two driver fixes - better parameter check for the core - Documentation updates - part of a tree-wide HAS_DMA cleanup * 'i2c/for-current' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux: i2c: sprd: Fix the i2c count issue i2c: sprd: Prevent i2c accesses after suspend is called i2c: dev: prevent ZERO_SIZE_PTR deref in i2cdev_ioctl_rdwr() Documentation/i2c: adopt kernel commenting style in examples Documentation/i2c: sync docs with current state of i2c-tools Documentation/i2c: whitespace cleanup i2c: Remove depends on HAS_DMA in case of platform dependency
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/i2c/dev-interface32
1 files changed, 14 insertions, 18 deletions
diff --git a/Documentation/i2c/dev-interface b/Documentation/i2c/dev-interface
index d04e6e4964ee..fbed645ccd75 100644
--- a/Documentation/i2c/dev-interface
+++ b/Documentation/i2c/dev-interface
@@ -9,8 +9,8 @@ i2c adapters present on your system at a given time. i2cdetect is part of
the i2c-tools package.
I2C device files are character device files with major device number 89
-and a minor device number corresponding to the number assigned as
-explained above. They should be called "i2c-%d" (i2c-0, i2c-1, ...,
+and a minor device number corresponding to the number assigned as
+explained above. They should be called "i2c-%d" (i2c-0, i2c-1, ...,
i2c-10, ...). All 256 minor device numbers are reserved for i2c.
@@ -23,11 +23,6 @@ First, you need to include these two headers:
#include <linux/i2c-dev.h>
#include <i2c/smbus.h>
-(Please note that there are two files named "i2c-dev.h" out there. One is
-distributed with the Linux kernel and the other one is included in the
-source tree of i2c-tools. They used to be different in content but since 2012
-they're identical. You should use "linux/i2c-dev.h").
-
Now, you have to decide which adapter you want to access. You should
inspect /sys/class/i2c-dev/ or run "i2cdetect -l" to decide this.
Adapter numbers are assigned somewhat dynamically, so you can not
@@ -38,7 +33,7 @@ Next thing, open the device file, as follows:
int file;
int adapter_nr = 2; /* probably dynamically determined */
char filename[20];
-
+
snprintf(filename, 19, "/dev/i2c-%d", adapter_nr);
file = open(filename, O_RDWR);
if (file < 0) {
@@ -72,8 +67,10 @@ the device supports them. Both are illustrated below.
/* res contains the read word */
}
- /* Using I2C Write, equivalent of
- i2c_smbus_write_word_data(file, reg, 0x6543) */
+ /*
+ * Using I2C Write, equivalent of
+ * i2c_smbus_write_word_data(file, reg, 0x6543)
+ */
buf[0] = reg;
buf[1] = 0x43;
buf[2] = 0x65;
@@ -140,14 +137,14 @@ ioctl(file, I2C_RDWR, struct i2c_rdwr_ioctl_data *msgset)
set in each message, overriding the values set with the above ioctl's.
ioctl(file, I2C_SMBUS, struct i2c_smbus_ioctl_data *args)
- Not meant to be called directly; instead, use the access functions
- below.
+ If possible, use the provided i2c_smbus_* methods described below instead
+ of issuing direct ioctls.
You can do plain i2c transactions by using read(2) and write(2) calls.
You do not need to pass the address byte; instead, set it through
ioctl I2C_SLAVE before you try to access the device.
-You can do SMBus level transactions (see documentation file smbus-protocol
+You can do SMBus level transactions (see documentation file smbus-protocol
for details) through the following functions:
__s32 i2c_smbus_write_quick(int file, __u8 value);
__s32 i2c_smbus_read_byte(int file);
@@ -158,7 +155,7 @@ for details) through the following functions:
__s32 i2c_smbus_write_word_data(int file, __u8 command, __u16 value);
__s32 i2c_smbus_process_call(int file, __u8 command, __u16 value);
__s32 i2c_smbus_read_block_data(int file, __u8 command, __u8 *values);
- __s32 i2c_smbus_write_block_data(int file, __u8 command, __u8 length,
+ __s32 i2c_smbus_write_block_data(int file, __u8 command, __u8 length,
__u8 *values);
All these transactions return -1 on failure; you can read errno to see
what happened. The 'write' transactions return 0 on success; the
@@ -166,10 +163,9 @@ what happened. The 'write' transactions return 0 on success; the
returns the number of values read. The block buffers need not be longer
than 32 bytes.
-The above functions are all inline functions, that resolve to calls to
-the i2c_smbus_access function, that on its turn calls a specific ioctl
-with the data in a specific format. Read the source code if you
-want to know what happens behind the screens.
+The above functions are made available by linking against the libi2c library,
+which is provided by the i2c-tools project. See:
+https://git.kernel.org/pub/scm/utils/i2c-tools/i2c-tools.git/.
Implementation details